1. Field of the Invention
This disclosure relates to a belt conveying apparatus configured to circulate an endless belt in a state of being stretched by a plurality of stretching members, and an image forming apparatus such as a printer or a copying machine provided with the belt conveying apparatus and employing an electrophotographic system.
2. Description of the Related Art
In the related art, examples of known image forming apparatuses configured to output color images include a tandem type image forming apparatus including a plurality of photoconductive drums arranged along an intermediate transfer belt. The image forming apparatus provided with the intermediate transfer belt is configured to form toner images having different colors on the photosensitive drums respectively, superimpose these toner images on the intermediate transfer belt in sequence as a primary transfer to form a color toner image. Subsequently, the image forming apparatus transfers the color toner image to a transfer medium passing between the intermediate transfer belt and a secondary transfer roller that is in contact with the intermediate transfer belt as a secondary transfer to output a color image on the transfer medium.
The color image forming apparatuses as described above generally have a color mode in which images are formed by using toners in four colors (yellow, magenta, cyan, and black) and a monochrome mode in which images are formed by using a toner in one color (generally, black toner). In the color mode, the primary transfer is performed by bringing all the photosensitive drums into contact with the intermediate transfer belt. In the monochrome mode, the primary transfer is performed by bringing only one of the photosensitive drums (generally, the photosensitive drum for black color) into contact with the intermediate transfer belt while separating the other photosensitive drums from the intermediate transfer belt. In this configuration, components to be used in image formation (for example, the photosensitive drums, a developer, and so forth), which are not involved in monochrome image formation, are not consumed unnecessarily.
As an example of configurations, which can select one of the monochrome mode and the color mode as described above by switching a contact state of the respective photosensitive drums with the intermediate transfer belt, Japanese Patent Laid-Open No. 2007-79570 discloses a configuration that is provided with a separating unit configured to move a plurality of the transfer members for the primary transfer arranged corresponding to the respective photosensitive drums.
However, the configuration disclosed in Japanese Patent Laid-Open No. 2007-79570 needs to provide a specific drive source for moving the transfer members. Therefore, a space for arranging the specific drive source is necessary, and hence reduction in size of the belt conveying apparatus is difficult when the drive source is provided in the belt conveying apparatus. In a case where the drive source is provided in an apparatus body, a specific space for the drive source is needed in the apparatus body, and hence reduction in size of the apparatus body is difficult.